feat(automation): add SQLAlchemy models for the three v1 tables

Three enums (one file each) plus three models (one file each), all
under app/automations/persistence/. The module imports from app.db
only (Base/BaseModel/TimestampMixin and FK targets searchspaces.id /
user.id); no business-logic imports.

Enums:
  - AutomationStatus: active | paused | archived
  - RunStatus: pending | running | succeeded | failed | cancelled
    | timed_out
  - TriggerType: schedule | manual (Phase-2/3 add webhook | event)

Models:
  - Automation: search_space-scoped, created_by_user_id (SET NULL),
    name + description, status enum, definition JSONB, version int,
    updated_at with onupdate.
  - AutomationTrigger: FK → automations (CASCADE), type enum, config
    JSONB, enabled bool, last_fired_at. Webhook secret_hash is omitted
    until Phase 2.
  - AutomationRun: FK → automations (CASCADE), nullable trigger_id
    (SET NULL — null = manual via UI), status enum,
    definition_snapshot for immutable history, trigger_payload /
    resolved_inputs / step_results / output / artifacts / error JSONB
    columns, started_at / finished_at timestamps, agent_session_id for
    linking to the LangGraph trace. cost_usd column omitted until at
    least one v1 capability records token-level cost.

Verified: Base.metadata exposes all three table names; columns and
enums introspect as documented; no linter errors.

surfsense_backend/app/automations/persistence/enums/run_status.py

@@ -0,0 +1,28 @@
+"""``RunStatus`` — the state machine of a single ``AutomationRun``."""
+
+from __future__ import annotations
+
+from enum import StrEnum
+
+
+class RunStatus(StrEnum):
+    """Lifecycle states of an ``AutomationRun`` row.
+
+    Transitions are linear with three terminal branches:
+
+        pending → running → (succeeded | failed | cancelled | timed_out)
+
+    ``pending``    — row created, executor task enqueued, work not started.
+    ``running``    — executor has picked up the run.
+    ``succeeded``  — terminal: plan completed without error.
+    ``failed``     — terminal: at least one step raised an unrecoverable error.
+    ``cancelled``  — terminal: caller asked for cancellation.
+    ``timed_out``  — terminal: run exceeded its configured timeout.
+    """
+
+    PENDING = "pending"
+    RUNNING = "running"
+    SUCCEEDED = "succeeded"
+    FAILED = "failed"
+    CANCELLED = "cancelled"
+    TIMED_OUT = "timed_out"